Feedback phase modulation receiver



will l6, 194U. cRosBY 2,197,518

FEEDBACK PHASE MODULATION RECEIVER Filed Oct. 7, 1938 4 Sheets-Sheet 1 70 AFC AM/D AF our-pur 1 o 0000000o \r 0000000 j R. E AMPLIFIER, 0157: AND I 1-". AMPL /LOCAL OSCILLATOR L INVENTOR.

. MURRAY 6.. CROSBY BY A TTORNEY.

rfl w, 1940 M. G. CROSBY 5 FEEDBACK PHASE MODULATION RECEIVER c c f x X U l U L v fix MM k U L L INV EN TOR. MURRA Y 6. CROSS Y BY gm A TTORNEY.

A ril 16, 19400 M. s. CROSBY FEEDBACK PHASE MODULATION RECEIVER Filed Oct. '7, 1938 4 Sheets-Sheet 3 INV EN TOR. MURRA Y 6. CROSBY 71$ A TTORNEY.

4 Sheets-Sheet 4 M. G. CROSBY FEEDBACK PHASE MODULATION RECEIVER Filed Oct. 7, 1938 A rfl 16,1940;

INVENTOR. MURRAY 6. CROSBY v A TTORNEY.

Patented Apr. 16, 1940 UNITED STATES PATENT OFFiCE Murray G. Crosby, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application October 7, 1938, Serial No. 233,719

19 Claims.

This application concerns new and improved phase modulation receivers in which inverse feedback is utilized to reduce the degree of phase modulation applied to the phase modulation detecting system of the receiver. In phase modulation detectors known heretofore the amount of phase deviation which they will handle is limited. My invention provides a phase modulation receiver which has increased capabilities with regard to depth or degree of phase modulation.

In the phase modulation receivers of this disclosure the output voltage from the detecting system is fed back to a phase modulation circuit which precedes the detecting system. Thus, when the incoming wave is phase modulated the voltage resulting from demodulation appearing at the detector output is applied to this phase modulator circuit preceding the detecting system with such a polarity that the effective phase deviation of the modulated wave applied to the detectors is reduced. For a given degree of phase deviation such a reduction of deviation applied to the detecting system will reduce distortion since the maximum demodulation capabilities of the detecting system are not reached.

This same feature may be utilized to allow a higher degree of modulation of the wave to be applied to the receiver to permit a wideband phase modulation of the wave used in the system. Thus the depth of modulation may be increased at the transmitter so that a noise recluction may be effected. In the receivers of the prior art this reduction has been accomplished by means of frequency division by multivibrators at the receiver as described in my United States application Serial No. 107,336, filed October 24, 1936. The method of the present disclosure allows the use of wide band phase modulation without the use of multivibrators which in some cases are somewhat unstable.

In a modification the potentials from the output of the phase modulated wave demodulator are passed through a circuit which modifies their amplitude so that they vary in amplitude directly in accordance with frequency. These potentials then frequency modulate (instead of phase modulating) the oscillator supplying heterodyne current to the second detector. In this manner the phase deviations on the wave are reduced.

In the several modificationsthe polarity of the potentials supplied by the detectors to the modulator may be such as to additionally phase modulate the received wave. That is, the degree or depth of phase modulation may be increased if desired as well as decreased.

In describing my invention more in detail reference will be made to the attached drawings; wherein Figure 1 shows a phase modulated wave receiver with means for unmodulating or further modulating the received wave to thereby control its degree of phase modulation as desired;

Figures 3 and 4 are diagrammatic showings of 10 modifications of the arrangement of Figure 1; while Figures 2a to 2h are vector diagrams used in illustrating the operation of the detectors m of the present invention.

The circuit of Figure 1 shows a specific embodiment of my invention in which neutralizing through coupling tubes, as described in my United States application Serial No. 165,056, filed September 22, 1937, now Patent #2,156,374, is- 20 sued May 2, 1939, is utilized in the means for converting the phase modulated current to amplitude modulated current for detection.

To simplify the description of the basic prin ciple of my method and means it is assumed that by the use of heterodyning'means known in the art and comprising signal pick 'up means I, radio frequency amplifying and detecting means 2 and local oscillat'or'3, phase or amplitude modulated wave energy has been reduced in 3 frequency, amplified in 2 if desired, and is impressed at intermediate frequency on the input electrodes of an amplifying tube 4 and from the output 5 of tube 4 on the grid 1 of a coupling tube 6 from the output electrode 9 of which it is impressed on the primary winding ill of a transformer I! having a secondary winding i2. The primary winding I0 is shunted and properly clamped by a resistor 18. and tuned by a variable condenser 20. wise properly damped by a resistor l9 in shunt thereto and is tuned by a variable condenser 22. By properly adjusting the coupling, tunings, and dampings of this transformer, it is made to have a band pass characteristic so that all of the frequencies of the phase modulated wave are passed thereby uniformly.

The secondary winding l2 has its terminals connected as shown to a piezo electric crystal 30 and a variable capacity 32 which with coupling tube 33 serves as means for neutralizing, under-neutralizing, or over-neutralizing the crystal 3B. In this particular case the crystal is over-neutralized by condenser 32 and coupling tube 33. The crystal 30, and capacityti! con- The secondary winding 42 is like- 40 tube 33 are tied together as nect the control grids 34 and 36 of electron discharge tubes 3| and 33 to winding i2, as shown, to feed wave energy thereto from I 2. The energy passed by the crystal 30 is amplified by the electron discharge tube 3|, while the neutralizing energy passed by coupling tube 33 is amplified by the electron discharge tube 33. The anode 38 of tube 3| and the anode 40 of shown and connected to the tuned primary winding 42 of a transformer 44. The capacity of the holder for the crystal 30 is neutralized, over-neutralized, or under-neutralized as desired by the neutralizing condenser 32 acting through coupling tube 33.

The winding 42 is tuned'by a condenser M. The secondary winding 46 of transformer M, tuned by condenser 4?, is connected as shown to the electrodes of a diode rectifier 50. The combination of the current passed by crystal 39 and tube 3!, and capacity 32 and tube 33 takes place in the primary winding of transformer M. Resistors 45 and 43 furnish a direct current connection to ground for the grid direct current circuits of tubes 3| and 33 while resistor 69, which is properly by-passed, furnishes self-bias to these tubes.

Modulated current which has been converted from phase modulation to corresponding amplitude modulated current for demodulation purposes is also taken from the terminal of crystal 30 and fed to the control electrode 52 of electron discharge tube 59. This current is passed by a filter which is underor un-neutralizecl. The anode 54 of coupling tube 59 is connected to the primary winding 56 of a transformer 58, the secondary winding 59 of which is connected to the electrodes of a diode rectifier 69. Windings 6 and 59 are tuned by condensers'55 and 5'! respectively,-and a damping resistance 70 is connected with winding 56.

Transformers I 7, M and 58 are band pass transformers with their tunings and dampings adjusted so that the center of the band passed is substantially equal to the mean frequency of the phase modulated current impressed on winding I0.

The transformer 58 in the plate circuit of tube 50 feeds the un-neutralized crystal energy to diode 60. By adjusting condenser 32 so that an over-neutralized crystal filter characteristic, as

to the intermediate frequency phase modulated wave energy, is obtained in transformer 44, detector 59 will be detecting energy passed by said filter of over-neutralized characteristics, whereas detector 68 will be detecting energy passed directly by 30, that is, energy passed by a filter having an unneutralized characteristic.

The diode resistors 6i and 63, which are bypassed by I. F. by-pass condensers as shown, are connected in series so as to differentially combine the detected outputs from the two transformers 44, 58. The resulting energy from these two resistors 6i and 63 is, if desired, fed to an automatic frequency control tube (for simplicity not shown here) which in turn may control the tuning of the high frequency oscillator 3 used to convert the received energy to intermediate frequency. A frequency control means as described here has been shown in my United States applications Serial No. 165,056, filed September 22. 1937, now Patent #2,156,374, issued May 2. 1939 and Serial No. 167,344, filed October 5, 1937, now Patent #2,156,375, issued May 2, 1939. Similar control circuits have also been disclosed in my prior United States Patents No. 2,065,565, dated December 29, 1936; No. 2,085,008, dated June 29, 1937; and application Serial No. 124,967, filed February 10, 1937.

Potentials from the high potential end of 6! are also supplied to the phase modulating 0r unmodulating means of the present invention. Potentials from 6! and 63 are also fed to an audio frequency amplifier to produce the output characteristic of the phase modulations on the received wave.

In the operation of the receiver of Figure 1 two filter characteristics are produced to be fed to the two diode detectors 50 and 60. The energy fed from the crystal output terminal to amplifier 50 is un-neutralized crystal energy and "has a characteristic shown in Figure 2a. This energy appears in transformer 58. The characteristic of the energy present in transformer 44 is as shown in Figure 2e, being derived from a filter of the over-neutralized type such as is obtained by overneutralizing crystal 30 by means of neutralizing condenser 32. This is obtained by adjusting condenser 32 so that its capacity is greater than that of the crystal holder which holds crystal 363. These two crystal filter characteristics as shown in Figures 2a and 26 have reactance characteristics as shown in Figures 21) and 2 respectively.

In the case of Figure 2b a negative reactance is present on both sides of the carrier frequency. that is, the circuit would be capacitive on both sides of the carrier except for the very short interval near the carrier frequency. Since the reactance is capacitive in the frequency region in which the side bands are disposed and is resistive at the carrier frequency, the phase of the side bands will be shifted 90 with respect to the carrier. In Figure 2c the carrier and side bands of a phase modulated wave are shown. The carrier is marked C, the upper side band U and the lower side band L. The positive direction of rotation is taken as clockwise and the directions of rotation of the side bands with respect to the carrier are indicated by arrows attached to the side band vectors. Side bands of an order greater than I have been neglected due to their small amplitude and for simplicity of explanation. When the phase modulated wave of Figure 2c is passed to a filter having the characteristic of Figure 2a and the reactance characteristic of Figure 2b and side bands are shifted 90 with respect to the carrier so that the side band relation shown in Figure 2d is effected. With the relation of 2d between the carrier and side bands, the wave is an amplitude modulated wave.

There would also be an attenuation of the side-' bands which is not shown in Figure 2d. This conversion of the phase modulated wave to an amplitude modulated Wave takes place in transformer 17, crystal 30 and tube 50, and the converted energy appears in transformer 58.

The energy present in transformer M, is passed by crystal 30 and capacity 32 comprising a filter having an over-neutralized characteristic and having an input-output characteristic as shown in Figure 2e and having a reactance characteristic as shown in Figure 2]. Thus, the reactance of this last filter is positive or inductive on both sides of the carrier frequency except for a short interval near the carrier frequency. Consequently the side bands are shifted 90 in phase by this filter also, but in an opposite direction to the shift produced by filters having the characteristics shown in Figures 2a and 2). Hence, the

phase modulated wave as shown in Figure 29 is I" converted to an amplitude modulated wave as shown in Figure 2h. i

From an examination of Figure 2d andFig'ure 271 it can be seen that the side bands are approaching cancellation of the carrier in Figure 2d and are approaching aiding the carrier in Figure 271.. Thus, the envelope of the amplitude modulations produced by the two filters having characteristics as shown above are 180 apart and their detected output must be combined in a push-pull or series combination to reproduce the converted modulations instead of a parallel combination. This combination is effected in the diode circuit of Figure l by reversing the connections of one of the diode resistors 61 and 63 as shown and connecting the same inseries to produce the receiver output. Unwanted amplitude modulations on the wave received which are not converted to phase modulations by the action of the two filters including crystal 3b as described herein and in my United States Patent No. 2,085,008, dated June 29, 1937, have the same or substantially the same effect on the energies passed by both filters, and consequently due to the phase displaced combination of energies in resistors M and 93 cancel each other more or less completely. The unwanted amplitude modulations which are converted to characteristic phase modulations have no efiect in the diode detectors 59 and E0.

By an examination of the filter characteristics of Figures 2a. and 2e it can be seen that when the carrier frequency drifts the relative ampli" tudes of the two filter outputs varies differentially. That is, as the frequency drifts lower the utput of the filter of Figure 2e approaches the dip point whereas the output of the filter of Figure 20. reduces more gradually. This results in a differential action which produces differential detected energy which may be used for automatic frequency control purposes.

Turning now to the phase modulating or unmodulating method and means of the present invention, the manner in which potentials produced at 6| are used to narrow or widen the phase deviations on the wave will be described.

The phase modulator utilizes a reactance tube type of modulator comprising tube operated somewhat as' described in my United States application Serial No. 209,919, filed May 25, 1938. Intermediate frequency energy is applied to the input of tube 4 having tuned circuit 5 connected between its anode and cathode. Reactance tube 80 has its anode B2 and cathode 84 connected across tuned circuit 5 by connections 4' and 5 so that voltage applied to the injector grid 8| of tube 80 will vary the reactance between the electrodes 82 and 84 in a well known manner and thereby vary the tuning of circuit 5 and conse quently vary the phase of the voltage in tuned circuit 5. This phase varied voltage is fed through coupling condenser H to amplifier tube 6 which has the primary Winding ill of transformer IT. in its plate circuit. Resistors l8 and it properly damp the tuned transformer l l. The elements numbered I T to 63 described in detail hereinbefore comprise the phase modulated current converting and detecting means.

The currents or voltages resulting from the conversion and demodulation of the phase modulated wave or current appear across resistors 6| and 63 and are fed through lead 68 and radio frequency filter 69 to the injector grid 8! of the reactance tube 80. Blocking condenser 14 feeds voltage to the control grid of reactance tube 80 through .pl'iaseshifting elements RiCr. Resistor furnishes a direct current return for the cont'rol'grid'lQ.

In describing the operation of the receiver of Figure 1 phase modulated current having a phase deviation of will be assumed to be obtained tube 4 and transformer l1. Normally such a degree: of deviation would overload a phase modulation receiver of the crystal filter type shown here. However, by utilizing inverse feedback the detected phase modulation output at resistors Bi and 83 is caused to unmodulate the incoming wave in such a manner as to reduce the degree of modulationalready present on that wave. Thus, if the energy fed from the detectors through lead 68 causes the reactance tube 80 to impart a phase'modulation of 60 which has a polarity opposite to the 120 applied phase modulation, the effective depth of phase modulation amplified by tube 6 and fed by transformer I! to the detecting system will be 60. Such a depth of modulation would not overload the phase modulation converting system and detectors. Hence, for this particular illustration the modulation capabilities of the receiver have been doubled.

To obtain this unmodulation of the current in tube 4 the signal voltages supplied by resistors BI and. 63 are supplied to filter 69 and then to the grid 8| in a sense to produce in tuned circuit 5 a reactive change which will cause a phase shift of say 60 in a sense to oppose the original 120 phase shift.

If the polarity of the voltages supplied to grid 8| are of improper phase their phase can be reversed. That is, the automatic frequency control potentials and the inverse feedback potentials are in accordance with my invention maintained in the desired sense to control the fre quency' of the intermediate frequency wave and to, when desired, unmodulate the same.

Numerous means for obtaining the desired polarity of the control potentials in the feedback circuit to widen or narrow phase deviations may be devised. The following means are satisfactory for this purpose.

The polarity of the output of detector tubes 50 and 6|] (with respect to both the AFC potentials and the inverse feedback or IFB potentials) may be reversed by grounding the cathode of diode detector 60 and making the cathode of diode detector 50 the high potential point or by grounding,the cathode of diode detector til and making the cathode of diode detector 66 the high potential point. The gang switches S1 and S2 serve this purpose, that is, ground either diode and simultaneously connect the other diode to the lead running to the useful output, the automatic frequency control, and the feedback circuit. Thus by changing this connection proper polarity may be obtained for either the automatic frequency control or the intermediate frequency feedback circuits. For purposes of illustration, let us say the polarity is adjusted for the automatic frequency control operation. If, with this connection, the polarity of the intermediate feedback is Wrong, the condenser C1 in the phase shifting circuit of the reactance tube 80 may be replaced by the inductance L1 so that the reactive effects applied to the tuned circuit 5 have an effect opposite to that produced by the capacitance.

Alternative means and methods for changing the polarity of the intermediate feedback potentials have also been illustrated. Such means may take the form of a coupling and amplifying tube 75 90, connected in circuit by switches ss and-Si at contacts C to replace the direct connection between points B. A transformer 9I also serves this purpose, when connected by contacts A to replace the direct connection between contacts B and B. When the coupling tube and amplifier is used for reversing the feedback potentials, it may be, as illustrated inFigure 1, coupled at its input by coupling condenser 92 to contact C and at its output by anadditional coupling condenser 93 to the other contact C. Plate potential is supplied by impedance 94 and grid potential is supplied by impedance 95. I

The polarity of the detected output may also be reversed by feeding diode 60 from coupling transformer 44 and feeding diode 50 from coupling transformer 58. This interchanges the connections of the overand under-neutralized crystal filters so that both the automatic frequency control output and the modulation. output are reversed.

In operation the following procedure is used to adjust for proper polarity of AFC voltage and unmodulating voltage. Ganged switches S1, S2 are thrown up or down to set the proper polarity for the AFC regardless of the unmodulating potentials. The unmodulating potentials may then be set to their proper polarity by meansv of switches S3, S4 and S5. With switches S3, S4 on points B, the polarity of the Voltage fed to the injector grid of unmodulating reactance tube 80 is the same as that fed to the AFC. 'With the switches on point C, amplifier 90, with coupling condensers 92 and 93 and plate resistor 94, is connected in the circuit so that the well-known 180 degree phase shift of an amplifier tube is imparted to the unmodulating potentials. With the switches on point A, transformer 9| is connected in the circuit and may be connected to effect either zero or 180 degrees phase shift by reversing the connections to its terminals. Switch S5 is also capable of imparting a 180 degree phase shift to the polarity of the modulation which is caused by reactance tube 80. This is due to the fact that S5 either connects in condenser 01 to effect a leading phase angle to the feedback voltage of the reactance tube, or connects in inductance L1 to effect a lagging phase angle to the feedback voltage. The leading phase angle makes the reactance tube plate circuit appear as an inductance in parallel with tuned circuit 5 so that an increase in gain of the reactance tube causes a reduction of the total inductance in the tuned circuit. The lagging phase angle makes the reactance tube appear as a capacity in parallel with the tuned circuit so that an increase in gain of the reactance tube increases the total capacity. Since a reduction of the total inductance in the tuned circuit is a tuning opposite in direction to an increase in capacity, switch S will therefore perform the function of reversal of the polarity of the unmodulation which is applied by the potentials from the output of the phase modulation detecting system.

The circuits of Figure 3 and Figure 4 show alternative modifications in which double detection superheterodyne receivers are utilized. The inverse feedback potentials are applied to phase modulate the second beating oscillator by means of corrected frequency modulation in the case of Figure 3 and by means of phase modulation in the case of Figure 4.

In Figure 3 energy from antenna I00 is fed to a superheterodyne receiver, consisting of a radio frequency amplifier, first detector and high frequency oscillator I02, a band pass filter and amplifier I03 and a second detector I04. The beating oscillator I I5 produces oscillations which are frequency multiplied and limited at unit I01. The oscillator H5 has an oscillation generating and frequency determining circuit III coupled by condenser H8 and grid leak and condenser H9 between its grid and anode. Potential for operation is supplied by choke II 9. The reactance of circuit I I1 includes or is supplemented by the reactance tube I06. Reactance tube I09 is somewhat similar to the reactance tube 80 of Figure 1. In Figure 3, however, the reactance tube I06 controlled by potentials supplied at III is coupled to an oscillation generator comprising tube I5 and circuit II'I whereas the reactance tube 80 of Figure 1 is connected to the wave relaying circuit 5. The multiplied and limited oscillations are fed to detector I04 and beat with the wave from I03. Energy at the second intermediate frequency obtained from second detector I04 is fed to the phase modulation detecting system I 05. This phase modulation detector may be of any type such as, for example, the underand over-neutralized filter type as illustrated in Figure 1.

The output for the detecting system in I05 is available at H0 and is also fed through frequency correcting elements I08 and I09 and filter III to the reactance tube I06 to modulate the frequency thereof. Correction circuit I08, I09 attenuates the low audio frequencies with respect to the high audio frequencies so that the potentials applied from circuit I II to reactance tube I05 have their amplitudes proportional to their frequency. The frequency modulation of the oscillationsproduced in tube H5 and circuit H1 is converted into phase modulation thereof by means of condenser I09 and the resistance of potentiometer I08. The resistance of I08 is made low compared to the reactance of I09 so that the voltage fed to the modulating grid of the reactance tube I06 will be directly proportional to the audio frequency of the modulating potentials supplied by the output of the phase modulation detecting system. This correction converts the modulation applied to beating oscillator I I5 into phase modulation. The polarity of this phase modulation is adjusted so that the heterodyned wave in the output of detector I04 resulting from the beat between the beating oscillator and the incoming signal has its degree of phase modulation reduced with respect to that on the incoming signal. This frequency correction causes frequency modulation oscillator I06 to a supply phase modulated waves to unit I01. Unit I01 contains limiters for removing concomitant amplitude modulation undesirably introduced in the process of phase modulating oscillator H5 and also contains frequency multiplying stages for increasing the degree of phase modulation on the wave from oscillator I95. This oscillator energy is used as the beating oscillator for detector I04 so that the beat resulting between the incoming Wave and the oscillator energy will be phase modulated in the same accordance that the oscillator energy produced by H5 is modulated. Since the potentials applied to correction circuit I08, I 09 may be of such phase as to cause inverse feedback and thereby reduce the depth of modulation applied to detecting system I05, this system has the same advantage as the system of Figure 1 and in addition has the possibility of being able to increase the degree of inverse feedback by frequencymultiplying beating oscillator Ill) II5. Also by using corrected frequency modulation a high degree of phase modulation is possible, so that a high degree of inverse feedback is possible and a receiver capable of handling a high degree of wideband phase modulation is effected.

The elements of Figure 3, such as I00, I02, I03, I04, I05, I01 and H5 correspond with the elements of Figure 4 such as I00, I02, I03, I04. I05, I01 and H5. In Figure 4 the same advantage with regard to frequency multiplication (and consequent increase of the degree of inverse feedback) is present. This circuit is different from that of Figure 3 in that the inverse feedback potentials are fed to a phase modulator unit instead of to a frequency modulated oscillator. The audio frequency correction circuit I08 and I09 of Figure 3 is therefore unnecessary In the circuit of Figure 4, the second beating oscillator I is also modulated as in Figure 3, but a phase modulator is used instead of a corrected frequency modulator. The heating oscillator consists of tube I40 with crystal MI and tuned circuit I42. Link coupling I43 couples the oscillator output to tuned circuit I44 which is midtapped so that two voltages 180 degrees out of phase are available at its terminals. The resistance-capacity phase shifter I45, I46 shifts the phase of the voltage fed to the control grid I49 of modulator tube I41 so that it is degrees out of phase with the voltage supplied to it by the tuned circuit I44. The difierence in phase between the voltages fed to the control grids I49 and I50 of tubes I41 and I48 is therefore 180 degrees plus or minus 45 degrees which is 135 degrees or 225 degrees. Either 135 or 225 degrees is the optimum phase shift for this type of phase modulator in which two phase differentiated voltages are recombined in tuned circuit I5I after one of them has been amplitude modulated. More in detail, the phase displaced oscillations supplied by oscillator I40, link I43 and phase displacing circuits I44, I45 and I46 are applied to the grids of the amplifying and. modulating tubes I41, I40 to appear in the combined circuit I5 I. If we assume that these phase displaced oscillations are of constant amplitude, there will be produced in tuned circuit I5I oscillations of a phase determined by the phase displaced oscillations. The resultant oscillations will have a phase which is the, approximate mean of the phases of the oscillations of displaced phase, assuming they are of like amplitude. Now, if the amplitude of one of the phase displaced oscillations be changed, the resultant will obviously shift in phase through an angle limited by the angular displacement of the phase displaced oscillations. To accomplish this modulation of the oscillations amplified in modulators I41 and I40, I control the amplification of one of the tubes, as, for example, tube I41, in accordance with the modulating potentials. This is accomplished by impressing the modulating potentials on the electrode I49. Here, since it is desired to modulate or unmodulate the phase of phase modulated waves appearing in I04, I use for modulating purposes potentials derived from the output of the phase modulation source in I05. These potentials are supplied by line I68 to amplitude regulating resistor or potentiometer I53 and from said resistor I53 to electrode I 49 by way of filter circuit I52 which removes or eliminates from the modulating potentials of a frequency greater than the modulation irequency. The circuit arrangement, per se, is such polarity to unmodulate or additionally modulate phase modulated waves applied to the detector I05 as desired. That is, the phase modulations on the frequency multiplied energy supplied by I01 to I04 for beating purposes are such as to result in intermediate frequency waves wherein the original phase deviations are increased or decreased, as desired. In the event the potentials are not of the desired polarity, expedients such as described in connection with Figure 1 may be resorted to, to adjust the potentials to the desired polarity. I

In Figures 3 and 4 the phase detecting system of unit I05 has been omitted for the sake of clarity and simplicity. This detecting system maybe as illustrated in Figure 1, or any other detecting system having the desired characteristics may be used here.

In any of the above systems cascade phase modulation may be applied to increase the degree of inverse phase modulation, if desired. For instance, in the circuit of Figure 1 the energy fed' through line 58 could also be fed to the injector grid of I a second reactance tube which was placed across a tuned amplifier stage preceding tube 4. v

.It will be apparent that any type of phase modulator or any type of phase modulation de tecting system would be applicable to this type of circuit.

I claim:

' 1. In means for demodulating alternating electrical current the phase of which has been varied in accordance with signals, a phase modulated wave demodulator, means for applying said phase modulated current to said demodulator to produce therein potential variations characteristic of the phase variations of said current, and means for modulating the phase of said current in accordance with said potentials.

2. In means for demodulating alternating electrical current the phase of which has been varied through a wide range in accordance with signals, a phase modulated wave demodulator operative over a range of phase modulation less than said wide range, means for applying said phase modulated current to said demodulator to produce therein potential variations characteristic of the phase variations of said current, and means for unmodulating the phase of said phase modulated current in accordance with said potentials.

3. Means for demodulating phase modulated electrical wave energy comprising, phase modulated Wave energy detecting means, means for applying said phase modulated energy to said detecting means, means connected with said detecting means for deriving therefrom potentials characteristic of the phase deviations on said phase modulated wave energy, and means energized by said derived potentials for modulating the phase modulated wave energy to change its degree of modulation before it is applied to said detecting means.

4. Means for demodulating electrical wave energy phase modulatedto a high degree comprising in combination, phase modulated wave energy detecting means, means for applying said phase modulated energy to said detecting means, means connected with said detecting means for deriving therefrom potentials characteristic of the phase deviations on-said' phase modulated wave energy, and means energized by said derived potentials for unmodulating the phase modulated phase of which is modulated throu z,1 ee in accordance with si phase modulated wave dem impressing 'gree of modulation on said 01 modulator in said last nam deriving from potentials characteristic oi til tilt. time modulated energy, and means for additionally modulate the p said wave energy to c lation. hange 6. Means for demodulating wave energy the h a wide degnals comprising, a

odulator phase modulated means for the phase deviations impressing said derived potentials on said phase modulator in a sense to unmodulate the phase modulations on said wave energy to reduce the degree of modulation.

'7. In a system for demodulating wave energy the phase of which has been modulated in accordance with signals, a phase modulated wave demodulator, a local oscillator, heterodyning means connected with said local oscillator and energized by said phase modulated wave energy to produce a beat note, means for impressing said beat note on said demodulator, means for deriving from said demodulator potentials characteristic of the phase deviations on said wave energy, and potential distorting means for applying said derived potentials to said oscillator to control the frequency of oscillations thereof.

8. Means for demodulating wave energy the phase of which is modulated in accordance with signals comprising, a. phase modulated wave demodulator, heterodyning means including a local oscillator and a detector for reducing the frequency of said wave energy, means for impressing said energy of reduced frequency on said demodulator, means for deriving from the output of said demodulator potentials which vary in amplitude linearly in accordance with the phase deviations on said energy of reducedfrequency, and means for modulating the frequency of said local oscillator in a sense to additionally modulate the phase modulations on said wave energy to change the degree of modulation.

9. Means for demodulating wave energy the phase of which is modulated through a wide degree in accordance with signals comprising, a phase modulated wave demodulator, heterodyning means including a local oscillator and a detector for reducing the frequency of said Wave energy of a wide degree of modulation, means for impressing said energy of reduced frequency .on said demodulator, means for deriving from the output of said demodulator potentials which vary in amplitude linearly in accordance with the phase deviations on said energy of reduced frequency, and means for modulating the frequency of said local oscillator in a sense to unmodulate the phase modulations on said wave energy to I reduce the degree of modulation.

10. 'In a phase modulated wave demodulating system, a phase modulated wave demodulator, a

source of local oscil said phase modulat signals comprising, a phase modulated modulator, heterodyning means includi oscillator for e a local modulator in a sense to additionally modulate the phase modulations on said wave energy of reduced frequency to change the degree of modulation thereof.

12. Phase modulated wave receiving means comprising in combination, wave relaying phase modulated wave detecting means, means including a phase controlling variable reactance for applying a phase modulated wave to said detecting means, means connected with said detecting means for deriving therefrom potentials characteristic of the phase deviations on said phase modulated wave, and means connected with said reactance and energized by said derived potentials for varying said reactance in a sense to additionally modulate the phase modulated Wave applied by said relaying means to said detecting means to change its degree of modulation.

l3. Receiving means as recitedin claim 12 wherein, saidadditional modulation is in a sense to decrease the phase modulation on said Wave. 4

14. Receiving means as recited in claim 12 .wherein, said additional modulation is in a sense to increase the phase modulation on said wave.

15. Phase modulated wave receiving means comprising in combination, phase modulated wave detecting means of the balanced type, amplifying means for applying phase modulated waves to said detecting means, a reactance tube in shunt to said amplifying means, means con nected with said detecting means for deriving therefrom potentials characteristicof the phase deviations on said phase modulated wave, and

means for controlling the reactance of said tube in a sense to additionally modulate the phase modulated wave to reduce its degree of modulation.

16. In a system for deniodulating wave energy the phase of which has been modulated to a high degree in accordance with signals, a phase modulated wave demodulator of the differential output type, amplifying means including a variable reactance connected with said demodulator and energized by said phase modulated Wave energy, means for deriving from said demodulator potentials characteristic of the phase deviations on.

wave de- 5 ill ill

lated wave energy which includes the steps of, producing oscillatory energy, multiplying the frequency of said oscillatory energy, beating said wave energy with said oscillatory energy of multiplied frequency and controlling the phase or frequency of said oscillatory energy in accordance with the phase deviations on said wave energy.

18. The method of demodulating phase modulated wave energy which includes the steps of, beating said wave energy with oscillatory energy to produce a phase modulated resultant to be demodulated, producing potentials which vary directly in accordance with the frequency of the modulations on said resultant and controlling the frequency of the oscillatory energy in accordance with said produced potentials.

19. In a system for demodulating wave energy the phase of which has been modulated to a high degree in accordance with signals, a phase modulated wave demodulator, a circuit on which said wave energy is impressed, an electron discharge device having electrodes on which said wave energy is impressed in phase displaced relation to produce a reactive effect between electrodes of said device, a connection between said last named electrodes and said circuit to connect said reactive effect in said circuit which is thereby tuned to the frequency of said wave energy, a phase modulated Wave demodulator coupled to said cirmodulator.

MURRAY G. CROSBY. 

